This invention relates to an apparatus for controlling a stepping motor usable in various devices such as a throttle drive device of an automotive traction control system.
Japanese published examined Patent application No. 57-54613 discloses an air flow rate adjustment apparatus including a pulse motor driving a control valve. During a predetermined interval in a start, the motor is driven by a low-frequency pulse signal to generate a great torque. After the predetermined interval elapses, the motor is driven by a high-frequency pulse signal.
In the apparatus of Japanese Patent application No. 57-54613, during the predetermined interval, the motor speed is low since the motor is driven by the low-frequency pulse signal. Accordingly, if the predetermined interval is long, the motor is unsuitable for a control system required to have a quick response such as an automotive throttle valve control system. If the predetermined interval is extremely short, the torque output tends to be insufficient and thus the motor sometimes falls into hunting or racing. Especially, if the motor is used at a low temperature, the viscosity of grease in the motor is high and a starting motor torque is inadequate so that the motor sometimes fails to start.
In the apparatus of Japanese Patent application No. 57-54613, while the motor is driven by the high-frequency pulse signal, the duration of the drive pulse is extremely short and thus it is generally difficult to detect a malfunction of windings of the motor on the basis of the drive pulse.